1. Technical Field
The present invention relates to a thermal analyzer for measuring a physical change in a sample with a temperature change caused by heating the sample.
2. Description of the Related Art
Conventionally, as a technique of evaluating temperature characteristics of a sample, there has been employed a technique called thermal analysis for measuring a physical change of a sample along with its temperature change caused by heating the sample. A definition of thermal analysis can be found in JIS K 0129: 2005 “General rules for thermal analysis,” and thermal analysis, according to this definition, includes all techniques that measure the physical properties of a measurement target (sample) under program controlled temperatures. Five common thermal analysis methods are (1) Differential Thermal Analysis (DTA) that detects temperatures (temperature difference), (2) Differential Scanning calorimetry (DSC) that detects a heat flow difference, (3) Thermogravimetry (TG) that detects masses (weight change), (4) Thermomechanical Analysis (TMA) and (5) Dynamic Mechanical Analysis (DMA) that detect mechanical properties.
The thermal analyzer 1000 shown in FIG. 9 represents a known example of thermal analyzers. The thermal analyzer 1000 performs Thermogravimetry (TG), and, as required, Differential Thermal Analysis (DTA). This thermal analyzer is provided with: a furnace tube 900 which is formed in a cylindrical shape and has an outlet 900b, which is reduced in diameter, on a anterior end portion 900a; a cylindrical heating furnace 3 which surrounds the furnace tube 900 from the outside; sample holders 41 and 42 which are arranged in the furnace tube 900 and hold samples S1 and S2 via sample containers; a measurement chamber 30 which is connected air tight to a posterior end portion 900d of the furnace tube 900; and a weight detector 32 which is arranged inside the measurement chamber 30 to measure weight changes in the samples (cf. JP-A-11-326249, JP-A-2007-232479, and JP-A-7-146262). The thermal analyzer also includes: two supporting pillars 218 extending downward from the lower end of the heating furnace 3. The supporting pillars 218 are connected to a support base 200. A flange 700 is fixed to the outside of the posterior end portion 900d of the furnace tube 900, and a single supporting pillar 216 extends downward from the lower end of the flange 700. The supporting pillar 216 is also connected to the support base 200. The support base 200 and the measurement chamber 30 are mounted on a base 10. The support base 200 is allowed to advance and retreat in an axial direction O of the furnace tube 900 by a linear actuator 220.
The heating furnace 3 heats the sample holders 41 and 42 from outside of the furnace tube 900, and the weight detector 32 detects the weights of the samples S1 and S2 as they change with temperature.
Here, as illustrated in FIG. 10, when the samples S1 and S2 are to be set on the sample holders 41 and 42 or the samples S1 and S2 are to be replaced, the support base 200 is allowed to advance toward the front end side (to the left in FIG. 10) of the furnace tube 900 by the linear actuator 220 so as to allow the heating furnace 3 and the furnace tube 900 fixed to the support base 200 to advance. Accordingly, the sample holders 41 and 42 are exposed on a side closer to the rear end side than the furnace tube 900, and thus the samples S1 and S2 can be set therein or replaced.
However, when the thermal analyzer described above is used, although a desired thermophysical property value can be detected, there is a problem in that changes in the samples during thermal analysis cannot be visually observed. This is because the furnace tube 900 is generally formed of ceramics such as sintered alumina or heat-resistant metal such as Inconel (registered trademark) and the heating furnace 3 covers the furnace tube 900.
With respect to these conventional thermal analyzers, the Applicants of the present application have proposed, in US patent publication No. US 2013/235899 A1, a new thermal analyzer that includes a furnace tube formed of a transparent material, and in which the furnace tube is exposed by moving forward only the heating furnace for sample observation so that a sample can be observed from outside of the exposed furnace tube. It is also proposed in US 2013/235899 A1 to cover a part of the exposed furnace tube with a heat conducting member, and partially inserting the heat conducting member into the heating furnace to transfer the heat of the heating furnace to the exposed furnace tube, and maintain the sample in a heated state at the sample observation position.
However, since a quartz glass tube, a YAG ceramic tube, or the like is used as the transparent furnace tube described in US 2013/235899 A1, as a result of repeated measurement at a high temperature (for example, near 1100° C.), a loss of clarity may occur. Particularly, in a case where a quartz glass tube which is relatively cheap is used as the furnace tube, the loss of clarity becomes significant. In addition, when the clarity of the furnace tube is deteriorated, observation of the sample is impeded, and thus the furnace tube needs to be replaced.
In order to make uniform the heat distribution or heat conduction of the furnace tube in the heating furnace, the furnace tube and the heating furnace need to be concentrically fixed to each other by allowing the axial centers thereof to match with each other. However, a gap needs to be provided between the inner surface of the heating furnace and the furnace tube so as not to cause the furnace tube therein to be broken due to thermal expansion of the heating furnace, and in order to secure heat conduction from the heating furnace, the gap needs to be maintained at a low value of about 1.5 mm. Therefore, it is difficult to accurately maintain the gap whenever the furnace tube is replaced and to accurately fix the furnace tube to the heating furnace concentrically.